Support `\` as the sign of explicit line joining
Vala now doesn't support explicit line joining, this may be inconvenient in some cases especially for strings.
void main () {
string foo = "\
aaa
aaa
aaa");
// C supports this, but may not be recommended
var a_long_long_long_long_long_\
long_name = 1234;
var bar = 0b\
1111\
1110\
1101\
1100\
1011\
1010\
1001\
1000;
}
Edited by Zhou Qiankang